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Title: Orbital-occupancy versus charge ordering and the strength of electron correlations in electron-doped CaMnO 3

Abstract

The structural, electronic, and magnetic properties of mixed-valence compounds are believed to be governed by strong electron correlations. Here we report benchmark density-functional calculations in the spin-polarized generalized-gradient approximation (GGA) for the ground-state properties of doped CaMnO{sub 3}. We find excellent agreement with all available data, while inclusion of strong correlations in the GGA+U scheme impairs this agreement. We demonstrate that formal oxidation states reflect only orbital occupancies, not charge transfer, and resolve outstanding controversies about charge ordering.

Authors:
 [1];  [1];  [1];  [1];  [1];  [1]
  1. ORNL
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
931685
DOE Contract Number:
DE-AC05-00OR22725
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review Letters; Journal Volume: 99; Journal Issue: 3
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; CALCIUM OXIDES; MANGANESE OXIDES; ELECTRON CORRELATION; ELECTRONIC STRUCTURE; ORDER PARAMETERS; MAGNETIC PROPERTIES; DENSITY FUNCTIONAL METHOD; GROUND STATES; DOPED MATERIALS; VALENCE

Citation Formats

Luo, Weidong, Franceschetti, Alberto G, Varela del Arco, Maria, Tao, Jing, Pennycook, Stephen J, and Pantelides, Sokrates T. Orbital-occupancy versus charge ordering and the strength of electron correlations in electron-doped CaMnO3. United States: N. p., 2007. Web. doi:10.1103/PhysRevLett.99.036402.
Luo, Weidong, Franceschetti, Alberto G, Varela del Arco, Maria, Tao, Jing, Pennycook, Stephen J, & Pantelides, Sokrates T. Orbital-occupancy versus charge ordering and the strength of electron correlations in electron-doped CaMnO3. United States. doi:10.1103/PhysRevLett.99.036402.
Luo, Weidong, Franceschetti, Alberto G, Varela del Arco, Maria, Tao, Jing, Pennycook, Stephen J, and Pantelides, Sokrates T. Mon . "Orbital-occupancy versus charge ordering and the strength of electron correlations in electron-doped CaMnO3". United States. doi:10.1103/PhysRevLett.99.036402.
@article{osti_931685,
title = {Orbital-occupancy versus charge ordering and the strength of electron correlations in electron-doped CaMnO3},
author = {Luo, Weidong and Franceschetti, Alberto G and Varela del Arco, Maria and Tao, Jing and Pennycook, Stephen J and Pantelides, Sokrates T},
abstractNote = {The structural, electronic, and magnetic properties of mixed-valence compounds are believed to be governed by strong electron correlations. Here we report benchmark density-functional calculations in the spin-polarized generalized-gradient approximation (GGA) for the ground-state properties of doped CaMnO{sub 3}. We find excellent agreement with all available data, while inclusion of strong correlations in the GGA+U scheme impairs this agreement. We demonstrate that formal oxidation states reflect only orbital occupancies, not charge transfer, and resolve outstanding controversies about charge ordering.},
doi = {10.1103/PhysRevLett.99.036402},
journal = {Physical Review Letters},
number = 3,
volume = 99,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}
  • The electron structure of undoped LaMnO{sub 3} and slightly doped La{sub 1-x}Sr{sub x}MnO{sub 3} manganites has been calculated within the framework of a generalized tight binding method with explicit allowance for strong intraatomic electron correlations. According to the results of these calculations, the ground state in orbitally disordered undoped LaMnO{sub 3} ferromagnets would be metallic despite the Mott-Hubbard correlation gap in the spectrum of quasiparticles. Owing to the orbital ordering, the insulating state is stabilized in both antiferromagnetic and paramagnetic phases. In-gap states of a polaron nature with a spectral weight proportional to the dopant concentration have been found nearmore » the top of the valence band in La{sub 1-x}Sr{sub x}MnO{sub 3}. As the doping level increases, a metal state appears in the ferromagnetic phase, which has a metallic character for one spin subband and an insulating character for the other subband (representing the so-called half-metallic state)« less
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  • No abstract prepared.
  • We use a first-principles'' concentration-wave approach based on a finite-temperature, electronic density-functional, mean-field, grand potential of the random alloy to investigate the high-temperature atomic short-range order (ASRO) in Ni[sub 75]V[sub 25] and Pd[sub 75]V[sub 25] solid solutions. Experimentally, these similar alloys both develop [ital D]0[sub 22]-type long-range order at low temperatures but different ASRO at high temperatures. Our calculations describe the measured ASRO well. We compare these results with those found for a hypothetical Co[sub 75]Ti[sub 25] solid solution. Since this alloy orders directly from the melt into the [ital L]1[sub 2] phase, it should exhibit strong [ital L]1[sub 2]-likemore » ASRO, as we find in our calculations. We analyze the features in the calculated diffuse intensities in terms of various factors in each alloy's electronic structure. Because we have assumed that the atoms are fixed to the Bravais lattice, we discuss two additional examples, Al[sub 75]Ti[sub 25] and Ni[sub 50]Pt[sub 50], to show the limitations of neglecting atomic displacements. Notably, the Onsager cavity fields have been incorporated into the theory to conserve the diffuse scattering intensity over the Brillouin zone and to provide a better description of the long-ranged, electrostatic screening effects.« less
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